Portable micro-preconcentrator to facilitate chemical sampling and subsequent analysis

ABSTRACT

The disclosed embodiments relate to the design of a preconcentrator system for preconcentrating air samples. This preconcentrator system includes a plurality of preconcentrators that preconcentrate the air samples prior to chemical analysis, and a delivery structure comprising a manifold that selectively routes a sample airflow to the plurality of concentrators so that the plurality of preconcentrators receive a sample airflow concurrently or individually.

RELATED APPLICATIONS

This application claims priority under 35 U.S.C. § 119 to the followingU.S. provisional patent applications: Application No. 62/313,523, filed25 Mar. 2016; Application No. 62/313,481, filed 25 Mar. 2016;Application No. 62/313,527, filed 25 Mar. 2016; Application No.62/313,513, filed 25 Mar. 2016; Application No. 62/313,507, filed 25Mar. 2016; Application No. 62/313,517, filed 25 Mar. 2016; ApplicationNo. 62/313,432, filed 25 Mar. 2016; Application No. 62/313,442, filed 25Mar. 2016; Application No. 62/313,457, filed 25 Mar. 2016; ApplicationNo. 62/313,486, filed 25 Mar. 2016; Application No. 62/313,489, filed 25Mar. 2016; and Application No. 62/313,495, filed 25 Mar. 2016. Thecontents of the above-listed applications are incorporated by referenceherein in their entirety.

GOVERNMENT LICENSE RIGHTS

This invention was made with United States government support underGrant No. 1255915 awarded by the National Science Foundation and underGrant No. US-4791-15R awarded by the US-Israel Binational AgriculturalResearch and Development Fund. The United States government has certainrights in the invention.

BACKGROUND Field

The disclosed embodiments generally relate to systems for gathering andanalyzing chemical samples. More specifically, the disclosed embodimentsrelate to the design of a micro-preconcentrator, which facilitatesgathering and storing chemical samples to facilitate subsequentchemical-analysis operations.

Related Art

Chemical-analysis techniques, such as ion-mobility spectrometry (IMS)and gas chromatography (GC), presently make it possible to produceanalytic systems that are able to identify complex chemical compoundswith a high degree of accuracy. However, it is often difficult to testsamples for vapor-phase chemical compounds because of their diffuseconcentrations. This difficulty can be addressed by installing a“preconcentrator” at the front end of an analytical system tosignificantly enhance the detection performance by trapping andconcentrating analytes.

Recent technological developments are presently making it possible toproduce significantly smaller IMS and GC systems. This is making itpossible to deploy chemical-detection systems in the field instead of ina laboratory, which provides significant advantages in diverseapplications, such as detecting the presence of chemical weapons orhuman-breath analysis. However, corresponding portable preconcentratordesigns need to be developed to make such portable chemical-analysissystems practical.

SUMMARY

The disclosed embodiments relate to the design of a preconcentratorsystem for preconcentrating air samples. This preconcentrator systemincludes a plurality of preconcentrators that preconcentrate the airsamples prior to chemical analysis, and a delivery structure thatdelivers the air samples to the plurality of preconcentrators.

In some embodiments, the delivery structure allows the plurality ofpreconcentrators to receive a sample airflow concurrently orindividually.

In some embodiments, the delivery structure comprises a manifold thatselectively routes a sample airflow to the plurality of concentrators.

In some embodiments, the delivery structure comprises a rotatingcomponent that holds the plurality of preconcentrators, wherein therotating component is rotatable to move each preconcentrator into aposition to receive a sample airflow.

In some embodiments, the delivery structure connects the plurality ofpreconcentrators so that a sample airflow passes through the pluralityof preconcentrators in parallel.

In some embodiments, the delivery structure connects the plurality ofpreconcentrators so that a sample airflow passes through the pluralityof preconcentrators in series.

In some embodiments, the delivery structure controls a sampling time foreach of the plurality of preconcentrators.

In some embodiments, the preconcentrator system is integrated into anunmanned aerial system.

In some embodiments, a flight path of the unmanned aerial system iscontrollable to facilitate gathering samples of interest.

In some embodiments, the preconcentrator system includes at least onepump to facilitate propagating a sample airflow through the plurality ofpreconcentrators.

In some embodiments, different sorbent materials are used in theplurality of preconcentrators for different applications.

In some embodiments, the preconcentrator system further comprises one ormore heaters to trigger a release of absorbed compounds from the sorbentmaterial contained in the one or more preconcentrators.

In some embodiments, the preconcentrator system performs labelingoperations to label the gathered air samples.

In some embodiments, the preconcentrator system incorporates GlobalPositioning System (GPS) data into the gathered air samples.

The disclosed embodiments also relate to another design for apreconcentrator, comprising an etched substrate, wherein the etchedsubstrate includes: one or more channels for sample airflow; one or morecavities for holding a sorbent material; one or more inlet holes forsample airflow; one or more outlet holes for sample airflow; and one ormore heaters integrated into the etched substrate.

In some embodiments, the preconcentrator is constructed usingmicrofabrication techniques.

In some embodiments, the one or more heaters comprise resistive heaters.

The disclosed embodiments also relate to another design for apreconcentrator system, comprising a substrate that is micro-machined toinclude consecutive cavities containing sorbent material, wherein theconsecutive cavities are separated by micro-pillars. During a samplingoperation, a gas phase sample passes through the consecutive cavitiescontaining the sorbent material. The preconcentrator system alsoincludes a mouthpiece and a tube, which are coupled to thepreconcentrator for receiving human-breath samples.

In some embodiments, each of the consecutive cavities includes an inletand an outlet, wherein micro-pillars at the inlet and the outletfunction to support and contain sorbent material in the cavity.

In some embodiments, each of the consecutive cavities holds a differenttype of sorbent material.

In some embodiments, one or more of the consecutive cavities is usedwith a molecular sieve to retain water content from a sample.

In some embodiments, the preconcentrator system further comprises ahumidity sensor and/or a temperature sensor located at an inlet of thepreconcentrator to trigger a breath sample.

In some embodiments, the preconcentrator system further comprises anintegrated heater that triggers a release of absorbed compounds from thesorbent material.

In some embodiments, the integrated heater is controlled using afeedback-based temperature-control technique.

In some embodiments, the integrated heater includes electrodes that facethe sorbent material in the cavities to decrease power consumption.

In some embodiments, the integrated heater includes electrodes having afractal structure.

In some embodiments, the preconcentrator system further comprises a pumpto facilitate moving a sample through the preconcentrator system.

The disclosed embodiments also relate to another design for apreconcentrator system for preconcentrating gas samples for agriculturalapplications. This preconcentrator system comprises a substrate, whichincludes: one or more channels for accommodating a sample flow, whereinthe one or more channels are coated with a sorbent material so that thesorbent material can be exposed to the sample flow; and one or moreheaters for heating the sorbent material.

In some embodiments, the sample flow includes one or more of: gassamples outgassed from plants in a greenhouse; gas samples outgassedfrom plants in an orchard; gas samples obtained during post-harvesttransportation of agricultural products; and gas samples obtained duringpost-harvest storage of agricultural products.

In some embodiments, a sorbent type and a sampling temperature arecontrollable during sampling to promote capture of volatile organiccompounds of interest over extraneous chemicals.

In some embodiments, the preconcentrator system further comprises anexternal cooling supply.

In some embodiments, the one or more heaters trigger a release ofabsorbed compounds from the sorbent material.

In some embodiments, the one or more heaters are fabricated bydepositing a conductive material on the substrate.

In some embodiments, the one or more heaters uniformly heat an activearea.

In some embodiments, the preconcentrator system further comprises one ormore temperature sensors, and a feedback-based temperature controlsystem that uses readings from the one or more temperature sensors tocontrol the one or more heaters.

In some embodiments, the one or more channels comprisehigh-aspect-ratio, porous microstructures for holding the sorbentmaterial.

In some embodiments, the high-aspect-ratio microstructures includechannels that are about 300 micrometers tall and 10 micrometers wide.

In some embodiments, the preconcentrator system comprises multiplepreconcentrators.

In some embodiments, the multiple preconcentrators are programmable toseparately sample during different time slots.

In some embodiments, the one or more heaters are programmable to either:apply heat rapidly to instantly desorb chemicals from the sorbentmaterial; or apply heat gradually to control a release of differentcompounds at different times from the sorbent material.

The disclosed embodiments also relate to a system and method forcontrolling environmental parameters in a shipping container. During themethod, the system: gathers samples of compounds off-gassed fromproducts stored in the shipping container; uses a chemical detector tomeasure concentrations of volatile compounds-of-interest in the samples;and performs closed-loop control of at least one environmental parameterin the shipping container based on the measured concentrations.

In some embodiments, the at least one environmental parameter includesone or more of the following: temperature, humidity, air ventilationrates, atmospheric gas composition, and light.

In some embodiments, using the chemical detector to measure theconcentrations of volatile compounds-of-interest includes using one ormore of the following: a gas chromatograph; an ion mobilityspectrometer; a differential mobility spectrometer; a high asymmetriclongitudinal field ion mobility spectrometer (HALF-IMS); a high fieldasymmetric ion mobility spectrometer (FAIMS); an electronic nose(E-nose); and an ethylene detector.

In some embodiments, controlling the at least one environmental variableincludes controlling one or more of the following for the shippingcontainer: a refrigeration unit; a heater; a humidifier; a light source;and a ventilation system.

In some embodiments, the closed-loop control is performed to mitigatespoilage of the products stored in the shipping container.

In some embodiments, the closed-loop control is performed to reduceenergy usage in the shipping container.

In some embodiments, the closed-loop control is performed to reduce theeffects of malodors on the products stored in the shipping container.

In some embodiments, the closed-loop control is performed to optimize aripening process for the products stored in the shipping container.

In some embodiments, the method further comprises using the measuredconcentrations of the volatile compounds-of-interest to detect diseasecontamination in the products stored in the shipping container.

In some embodiments, the method further comprises producing a log ofvolatile compound concentrations monitored during a shipment involvingthe shipping container.

In some embodiments, the method further comprises: determining from themeasured concentrations of the volatile compounds-of-interest whetherthe products stored in the shipping container have spoiled; and if theproducts have spoiled, discontinuing the power used to control the atleast one environmental parameter.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 illustrates a chemical-analysis system in accordance with thedisclosed embodiments.

FIG. 2 presents a photograph of an exemplary chemical-analysis system inaccordance with an embodiment of the present disclosure.

FIG. 3 presents a flow diagram for a chemical-analysis system in anunmanned aerial system (UAS) in accordance with the disclosedembodiments.

FIG. 4A illustrates a sampler cartridge system in accordance with thedisclosed embodiments.

FIG. 4B illustrates a sampler array system in accordance with thedisclosed embodiments.

FIG. 5A presents a photograph of an exemplary preconcentrator inaccordance with the disclosed embodiments.

FIG. 5B presents a photograph illustrating etched micro-pillars in anexemplary preconcentrator in accordance with the disclosed embodiments.

FIG. 5C presents a diagram of a resistive heater and temperature sensorpattern for a preconcentrator in accordance with the disclosedembodiments.

FIG. 6 presents a flow chart illustrating operations performed by apreconcentrator in accordance with the disclosed embodiments.

FIG. 7 illustrates a shipping container with a closed-loop environmentalcontrol system in accordance with the disclosed embodiments.

FIG. 8 illustrates a closed-loop environmental control system inaccordance with the disclosed embodiments.

FIG. 9 presents a flow chart illustrating operations performed by aclosed-loop environmental control system within a shipping container inaccordance with the disclosed embodiments.

DETAILED DESCRIPTION

The following description is presented to enable any person skilled inthe art to make and use the present embodiments, and is provided in thecontext of a particular application and its requirements. Variousmodifications to the disclosed embodiments will be readily apparent tothose skilled in the art, and the general principles defined herein maybe applied to other embodiments and applications without departing fromthe spirit and scope of the present embodiments. Thus, the presentembodiments are not limited to the embodiments shown, but are to beaccorded the widest scope consistent with the principles and featuresdisclosed herein.

The data structures and code described in this detailed description aretypically stored on a computer-readable storage medium, which may be anydevice or medium that can store code and/or data for use by a computersystem. The computer-readable storage medium includes, but is notlimited to, volatile memory, non-volatile memory, magnetic and opticalstorage devices such as disk drives, magnetic tape, CDs (compact discs),DVDs (digital versatile discs or digital video discs), or other mediacapable of storing computer-readable media now known or later developed.

The methods and processes described in the detailed description sectioncan be embodied as code and/or data, which can be stored in acomputer-readable storage medium as described above. When a computersystem reads and executes the code and/or data stored on thecomputer-readable storage medium, the computer system performs themethods and processes embodied as data structures and code and storedwithin the computer-readable storage medium. Furthermore, the methodsand processes described below can be included in hardware modules. Forexample, the hardware modules can include, but are not limited to,application-specific integrated circuit (ASIC) chips, field-programmablegate arrays (FPGAs), and other programmable-logic devices now known orlater developed. When the hardware modules are activated, the hardwaremodules perform the methods and processes included within the hardwaremodules.

Various modifications to the disclosed embodiments will be readilyapparent to those skilled in the art, and the general principles definedherein may be applied to other embodiments and applications withoutdeparting from the spirit and scope of the present invention. Thus, thepresent invention is not limited to the embodiments shown, but is to beaccorded the widest scope consistent with the principles and featuresdisclosed herein.

Chemical-Analysis System

FIG. 1 illustrates an exemplary chemical-analysis system 100 inaccordance with the disclosed embodiments. During operation,chemical-analysis system 100 receives a sample airflow 102, which isdirected through a micro-preconcentrator 104, which traps andconcentrates analytes from the sample airflow 102. Next, the output ofmicro-preconcentrator 104 feeds into an ion-mobility spectrometer 106,which produces a set of measured values for analytes in thepreconcentrated sample to form a sample profile 110. As illustrated inFIG. 1, the output of micro-preconcentrator 104 can also feed into a gaschromatograph 108, which similarly measures values for analytes to addto the sample profile 110.

An exemplary implementation of chemical-analysis system 100 isillustrated in the photomicrograph that appears in FIG. 2. Asillustrated in FIG. 2, the system includes a micro-preconcentratorcomprising a preconcentrator cavity 206 and a heater 208. The output ofthis micro-preconcentrator feeds into an ionization pathway 204 and theninto an ion-mobility spectrometer 202.

We now describe a number of application-specific variations of thechemical-analysis system 100 illustrated in FIGS. 1 and 2. Inparticular, we describe implementations associated with: (1) an unmannedaerial system (UAS), (2) a portable human-breath analyzer, and (3) aportable system for gathering agricultural samples.

Unmanned Aerial Vehicle Implementation

As mentioned above, a chemical-analysis system can be attached to anaerial platform (such as an unmanned aerial system (UAS), an airplane ora helicopter) and be used to sample, preconcentrate, separate, ionize,detect/measure and report on chemicals of interest as the aerialplatform moves across space and time. This system can include any or allof the modules illustrated in FIG. 3, although the order and combinationof these modules can be rearranged for a specific application. At theheart of this system is a chemical-detection module, which can comprisea HALF-IMS, but it might contain other detectors, including duplicateHALF-IMS modules, or IMS, DMS, FAIMS, IR, FTIR or other single-chemicaldetection modules.

As illustrated in FIG. 3, an air sample 302 can be gathered by variouspassive or active mechanisms to bring an ambient air sample into thesystem for chemical analysis. These mechanisms can include: pumps, fans,and a system that creates static pressure differences, such as placementof an inlet in a flow field across an airfoil, etc. Preconcentrators 304and 314 are used to preconcentrate gas-phase samples, which areencountered during the movement of the UAS. Preconcentrators 304 and 314can include multiple micro-preconcentrators or miniaturepreconcentrators (μPC), which can be used to gather and store samplesfor future lab analysis, or alternatively can be coupled to one or moreseparators, ionization sources and detectors to provide real-timechemical analysis while in-flight. When stored on a preconcentrator, theair sample can be saved for forensic analysis at a later time. A pumpcan be used to move a sample into the adsorbing material of thepreconcentrator. Factors such as sorbent type and device temperatureduring sampling can be controlled to promote capture of volatilecompounds-of-interest over extraneous chemicals. Moreover, eachpreconcentrator can include an integrated heater to force release of thecollected compounds to the ionization source/detector or lab system. Thesystem can be powered via batteries or using the aerial system's powersupply. Also, the preconcentrator can be produced using low-cost etchingtechniques involving glass substrates, or it can be fabricated ontometals, silicon or other substrates.

Multiple preconcentrators can be coupled and used in a single system,which allows each preconcentrator to sample separately or together as agroup in parallel. This is particularly useful for UAS applications. TheUAS can be programmed to sample at several geolocations separately witha different preconcentrator designated for each location and/or timepoint.

A control system provides instructions and feedback 326 for missionplanning. For example, the UAS can be trained to follow increasingconcentrations of chemicals. Moreover, the mission planning can be basedon biologically inspired search techniques. Also, the chemicalmonitoring and/or sampling can be constant or intermittent.

The preconcentrator can be micro-fabricated along with a detector tomake a multi-component system on a single chip. Moreover, the detectorcan feature one or more chemical detectors, such as anion-mobility-spectrometry-based system containing an ionization source,a drift tube, and a current meter. An exemplary detector is a HALF-IMS.

The system can look for all chemicals present in a sample, or it canonly look for chemicals that are of interest and are pre-programmed. Itcan also screen for types of chemicals (e.g. classes of chemicals), oruniquely identify them.

The sensing system components include a sampler, a preconcentrator, amicrocontroller, at least one HALF-IMS, and a possible separationmodule. It can also include other types of chemical sensors. The systemcan additionally include other non-chemical sensors to detect: light,pressure, flow, humidity, etc. The system can also be designed to limitsize and power requirements as allowed by the carrying aircraft.

The preconcentrator can be fabricated on low-cost glass substrates usingtraditional lithography along with wet-etching techniques to create amicro-channel for sample flow and a cavity to hold sorbent material. Itcan be alternatively manufactured on other substrates, and/or usingother manufacturing techniques. The sorbent material can becarbon-powder-based, and can be chosen for a specific application ofinterest. A metalized pattern of electrodes on the back or front side ofthe preconcentrator comprises a resistive heater and temperature probesfor each preconcentrator. A low-cost metal, such as tungsten, can beadvantageously used to implement these electrodes due to its relativelyclose coefficient of thermal expansion to glass (4.3 versus 3.25 μm/mK), durability, and high temperature performance characteristics. Toreduce the effects of oxidation, the tungsten film can be passivatedusing a thin layer of chromium. Note that other manufacturing methodscan be used, as well as other materials.

The use of directly deposited heaters provides an efficient method tocontrol the temperature of the sorbent bed. Depending on theapplication, heat can be applied rapidly to instantly desorb chemicalsin the sorbent trap, or gradually to raise the temperature of thesorbent bed to control the release of different compounds at differenttime periods.

In the embodiment illustrated in FIG. 4A, a set of preconcentrators isimplemented as a sampler cartridge system 400 comprising a movable“cartridge,” which features the arrangement of one or morepreconcentrators. Using a common pattern for air inlet/outlet locationson each preconcentrator, and perhaps embedded heaters, such as resistiveheaters created by deposited metal, enables the use of a single pump.The system can also filter to eliminate certain particle sizes. Notethat the system can move each sampler (comprising a preconcentrator) tointerface with the inlet 402 and the outlet 404. This can be done withpre-knowledge of the ambient conditions, or in response to chemicalinformation obtained from the system in-flight. Sampling time can becontrolled via a microcontroller such that when sampling to a givenpreconcentrator is complete, it is moved away from the airflow interfaceand is hermetically sealed for future sample extraction and analysis.The next preconcentrator can then be used for sampling. The geolocationand time of each sample can be recorded to facilitate creating a mapacross an area, which can be used to track a toxic plume or otherchemical emissions.

In a second embodiment illustrated in FIG. 4B, a sampler array system420 comprises an array of samplers (containing preconcentrators)421-426, which are linked in parallel using tubing and solenoids and/ora manifold 430 to vary flow into the devices across space and time.Unlike the previous embodiment, this embodiment does not include movingcomponents. Instead, a microcontroller (not shown) is used to specifywhich preconcentrator receives the sample airflow for a given timeperiod.

In both of the preconcentrator implementations described above, it ispossible to create a system that facilitates sampling to multiplepreconcentrators concurrently, or sequentially. This provides a way togather sample replicates when an application requires them. After thesample is collected, it can be returned to a base location wherechemicals retained on preconcentrators can be analyzed using traditionalbench top chemical-analysis techniques. The system can alternatively beinterfaced with a chemical-detection system, such as an ion mobilityspectrometer or a HALF-IMS, to perform real-time chemical analysis whilethe UAS is in-flight. A microcontroller can power and direct the heatersand the analysis can be performed after the sample is collected withoutrequiring user input, perhaps while the UAS is flying to its nextsampling location. Decisions on mission planning can be madeautonomously based on chemical information obtained in-flight.

Coupling the chemical detection system to a UAS provides additionaladvantages. The system can be powered using the UAS's power supply andcontrolled using the UAS's control system. This facilitates sampling atmultiple locations during a single flight, wherein a separatepreconcentrator can be used for each location. The preconcentrators canbe the same, or can have variations that are tailored for each samplinglocation or for increased sampling breadth. The flight path can beautomated by using GPS coordinates and timestamps for sampling locationsand prescribing the time for sampling at each sampling location. Afterthe sampling is complete, the UAS can return to a base location and thepreconcentrators can be taken to a lab for subsequent analysis. Variousapplications can make use of such sampling capabilities, including:surveying of farm land or other biological ecosystems, detection ofharmful or controlled substances, and air quality monitoring. Moreover,samples collected for later forensic use can be uniquely numbered (e.g.,barcoded) so that they can be tracked and the information can beassembled into a bigger picture of the surveyed region

The preconcentrator can be fabricated as a single chip with a detector,such as a HALF-IMS or an ion mobility spectrometer. In such anembodiment, the chip contains a sorbent bed and a channel forpreconcentration. Teflon film can be used to bond substrate halvestogether to form channels and/or interconnects between differentdevices. This process can be carried out by heating the film to ˜280° C.and applying approximately 5 PSI of pressure for five minutes. Theresult is a chip, which is amenable to multilayer structuring. Theoutflow from the preconcentration step can be ionized by an ionizationsource, and can be fed through a drift tube to a detector. The smalldevice feature size allows for a reduction of dead volume, therebyimproving the efficiency of analysis and reducing ion loss. Integratedheaters can also be used to ensure that the temperature is uniformthroughout the device channels, which allows analytes to remain in thegas phase and not condense on the channel walls due to local cool areas.

Specific features of the system include the following.

-   -   Materials/Fabrication: The preconcentrator can be made of glass        and can be filled with off-the-shelf sorbents. Metalized layers        (including tungsten) can help achieve temperature control.    -   Concentration Factor: A concentration in the range from        parts-per-trillion (ppt) to parts-per-billion (ppb) (a 1000×        concentration) can be achieved with a sampling time of 2 min.        However, if the sampling time is increased substantially        (e.g., >5 min), then a 10,000× concentration is possible. Note        that the amount of VOCs captured can be increased by        substantially increasing this sampling time.    -   Selectivity and Specificity: Selectivity to certain analytes can        be altered by changing the sorbent material used. A carbon-based        multi-purpose sorbent is suitable for a wide range of VOCs.        However, true specificity to a single analyte is difficult to        achieve with most sorbent materials used in preconcentration        devices; chemical separation and identification is typically        performed by the detection system.    -   Form Factor: The system can use a carrier gas in an outgas step        to ensure that the sample goes from the preconcentrator to the        detector. The preconcentrator and detector can also be        integrated into a single chip.    -   Power Usage: The system can be powered using a standalone        battery or can be coupled to the power supply of the UAS.

Portable Breath Analyzer Implementation

We now describe an implementation of a device called a “humiditymicro-preconcentrator (HuPC),” which is designed for human-breathsampling and is associated with a workflow for collecting volatileorganic compounds (VOCs) from complex mixtures in a high-humidityambient such as exhaled breath. An exemplary HuPC is illustrated in FIG.5A. The HuPC includes a number of novel design features, including: (1)an electrode arrangement that faces the adsorbent cavity to decreasepower consumption; (2) water rejection within a specifically designedmolecular sieve cavity; (3) inclusion of temperature and humiditysensors to trigger environmental or breath sampling conditions; (4)potential use of a fractal structure for metal electrodes; and (5) useof micro-pillar structures to define the cavities and as stoppers forthe adsorbents. Moreover, this HuPC device is designed to be portable,easy to use and inexpensive to manufacture.

The HuPC device is designed to collect VOCs from exhaled breath. A pumpcan be added at the rear of the HuPC to provide external pressure, whichis likely to be required during breathing from a resting state. The HuPCdevice can also include an inert polytetrafluoroethylene mouthpiece andtube connected to the micro-preconcentrator (HuPC), which can be made ofsilicon and inert glass using microfabrication techniques. However,other sampling materials and configurations can be used.

The portable HuPC device is designed to collect VOCs having differentchemical structures and polarities by using consecutive cavities, whichare separated by micro-pillars. As illustrated in FIG. 5B, deepmicro-channels (and associated micro-pillars) can be micro-machined inthe substrates using low-cost wet etchants or other microfabrication ormanufacturing techniques. These micro-pillars can be used as cavitydefiners and adsorbent stoppers. The glass can be used as enclosure andsupport for the micro heaters, and also for the humidity and temperaturesensors. However, other substrate materials can also be used. Moreover,different materials can be used for the electrodes, including platinum,gold or tungsten. Humidity and temperature sensors located at the inletare included to indicate when a breath sample is being collected. Theproposed sensing medium of the humidity sensor of the HuPC is polyimide,but other sensing media can be used.

It is possible to use off-the-shelf adsorbents, with a single adsorbentper cavity, or with multiple combinations of adsorbents, which can beused to adsorb/absorb specific compounds-of-interest. Additionally,multiple-stack HuPCs with single or multiple adsorbents are feasible.Also, one of the cavities can be used with a molecular sieve to retainthe water content of the sample. During system operation, the collectiontemperature can be maintained within a narrow range to ensuresample-to-sample reproducibility between breaths and between people. Thecollected VOCs can be subsequently desorbed and analyzed usingappropriate analytical chemistry techniques for the analyte composition.

Adsorbed compounds can be released from the HuPC by a thermal pulse orby ramping the temperature to have gas-chromatograph-like profilesprovided by a novel metal electrode design. In some embodiments, theelectrodes (and also the humidity and temperature sensors) are facingthe adsorbents, so less power is required to heat them. This removesunnecessary thermal mass in comparison to traditional electrodearrangements on the opposite side of the silicon or glass or othersubstrate.

With regard to materials and fabrication, the preconcentrator can bemade of silicon and glass (or other substrate) and can be filled withoff-the-shelf commercial sorbents. Custom sorbents for specificchemicals can also be used. Several cavities define the HuPC, whereineach cavity contains micro-pillars at the inlet and outlet that supportand contain the adsorbents. Electrodes comprising metalized layers canbe comprised of various materials, such as platinum, gold and tungsten(or other metal) to help to achieve temperature control. Note that theelectrodes face the cavities, which decreases the power required todesorb the retained VOCs. Optical energy can also be used fortemperature control. The capacitive humidity sensing material can bepolyimide, but different materials can be used.

Selectivity to certain analytes can be altered by changing the sorbentmaterial used. For example, different powder-based inorganic orcarbon-based multi-purpose sorbents can be used to enablepreconcentration of a wide range of VOCs of different sizes and chemicalstructures. Also, different adsorbents can be used to promote retentionof specific VOCs, and molecular sieve sorbents can be used to reducewater content.

This device can be connected in series with various components,including: chemical ionization sources, samplers, and chemical detectorsto facilitate near-real-time analysis. This device can also be used forforensic concentration and sampling of breaths for later analysis at adifferent location. The geolocation and time can be annotated tocorrespond with the breath sample.

This device can be also connected with a smart device or personal mobiledevice, such as a cell phone for breath sampling and monitoring. Thisdevice can also be tailored for other high-humidity ambient or containedenvironments, or for nonhuman (e.g., animal) breaths.

Advantages of the proposed breath micro-preconcentrator include: (1) thepossibility of miniaturization; it is expected that the device can bepackaged within a cell phone form factor; (2) the decreased powerconsumption resulting from design solutions of arranging the electrodesto face the adsorbent cavity; (3) the capability of operating in ahigh-humidity environment achieved by the water content rejection withina specific molecular sieve cavity; (4) inclusion of temperature andhumidity sensors to trigger ambient or breath sampling conditions; (5)usage of metal electrodes with a fractal structure (as illustrated inFIG. 5C) to increase the heating factor compared to plain or otherelectrode configurations; and (6) the use of micro-pillar structures todefine the cavities and serve as stoppers for the adsorbents. Finally,the device is designed to be portable, easy to use and inexpensive tomanufacture.

Agricultural Implementation

An alternative implementation is useful for agricultural applications,such as: detection of VOCs that are outgassed from plants in agreenhouse or an orchard setting; post-harvest monitoring and monitoringagricultural products during transport/storage/shipment; and assessingthe quality of an agricultural product, in terms of flavor or aroma.

This agricultural implementation can include one or moremicro-preconcentrators (μPC), which can each be used to gather and storea sample for future lab analysis. It can also be coupled to one or moremobile ionization sources and mobile detectors for real-time analysis ata point-of-testing. A pump can be used to move a sample into theadsorbing material of the μPC. Factors such as sorbent type and thedevice temperature during sampling can be controlled to promote captureof volatile organic compounds (VOCs) of interest over extraneouschemicals. Each preconcentrator can feature an integrated heater toforce release of the collected compounds to the ionizationsource/detector or lab system, with a design that uniformly heats theactive area. Each preconcentrator can also feature an integratedtemperature sensor for feedback-based temperature control, allowing fortemperature and time-based chemical separation, similar to a miniatureor full-sized gas chromatograph. An external cooling supply can also beused to allow for faster sampling ability. The system can be powered viabatteries, or an alternative portable method. The preconcentrator can befabricated using microfabrication etching techniques on a siliconsubstrate, or by finely controlled additive manufacturing techniques.Each preconcentrator can feature porous micro-structures for increasedsurface area, and can use microfabrication plating methods to coat anadsorbent material that is tailored to the specific analytes ofinterest.

In general, the preconcentrator can be fabricated using varioussubstrates, with traditional processing methods such as photolithographyalong with etching to create a micro-channel for sample flow and acavity with high-aspect-ratio porous microstructures to hold sorbentmaterial. Metalization can be used to pattern electrodes, which compriseheating elements and temperature probes for each preconcentrator. Theuse of directly deposited heaters provides an efficient method oftemperature control of the sorbent bed, but externally bonded componentscan be alternatively used. Depending on the application, heat can beapplied rapidly to instantly desorb chemicals in the sorbent trap, orcan be applied gradually to raise the temperature of the sorbent bed tocontrol the release of different compounds during different timeperiods. A low-cost metal such as tungsten can be used due to itsrelatively close coefficient of thermal expansion to silicon (4/0.3versus 2.6 μm/m K), durability, and high temperature performancecharacteristics. To reduce the effects of oxidation, the tungsten filmcan be passivated using a thin layer of chromium. Alternatively, goldmay be used during a plating step.

With regard to materials and fabrication, multiple preconcentrators canbe fabricated on a single substrate, and the channel for sample flow canbe created by etching. Patterned metalized layers (e.g., tungsten orgold) can be used to form a resistive heater network and atemperature-coefficient-of-resistance-based temperature sensor, allowingfor temperature control. Also, an external cooling supply can be used torapidly cool the device after thermal desorption, and a humidity sensorand a desiccant material may also be used to control moisture in thesample.

A concentration factor of greater than 1000× can be achieved for a shortsampling time on the order of 2 min. However, the amount of VOCscaptured can be further increased by substantially increasing thesampling time.

Moreover, selectivity to certain analytes can be altered by changing theadsorbent material. The adsorbent material is expected to be derivedfrom a thiol compound, but may also be Tenax TA, or a carbon-basedadsorbent. However, true specificity to a single analyte is difficult toachieve with most sorbent materials used in preconcentration devices.Note that chemical separation and identification is typically performedby the detection system. High levels of temperature control canpotentially be used for time-based separation of chemicals without anadditional gas chromatography system.

Also, a carrier gas can be used during an “outgas step” to ensure thatthe sample goes from the preconcentrator to the detector.

Process of Operating a Preconcentrator

FIG. 6 presents a flow chart illustrating operations performed by apreconcentrator in accordance with the disclosed embodiments. First, thesystem receives a sample airflow (step 602). Next, the system routes thesample airflow through a delivery structure to a set ofpreconcentrators, wherein each preconcentrator can include a differentsorbent material, and wherein the delivery structure routes the sampleairflow through the set of preconcentrators in parallel and/or in series(step 604). Finally, the system analyzes the preconcentrated samplesfrom the set of preconcentrators using one or more analysis modules todetermine chemical compositions of analytes in the sample airflow (step606).

Shipping Container

The above-described portable chemical-analysis system can be used in avariety of applications including in a closed-loop control system tocontrol environmental parameters within a shipping container, such as arefrigerated shipping container, which is used to transport perishableproducts. For example, FIG. 7 illustrates a shipping container 700 witha chemical-based closed-loop environmental control system in accordancewith the disclosed embodiments. As illustrated in FIG. 7, shippingcontainer 700 contains a shipped product 702, which is sensitive toenvironmental parameters, such as temperature and humidity. It alsoincludes a chemical sensor 704, which detects and analyzes off-gassedchemicals from shipped product 702. Readings from chemical sensor 704feed into a closed-loop controller 706, which uses the readings toperform closed-loop control of an environmental parameters modifier 708,such as a refrigeration unit, a heater, a humidifier, or a ventilator.

Closed-loop controller 706 is used to implement a closed-loop controlsystem, which uses chemical sensor 704 to monitor volatile compounds,especially volatile organic compounds (VOCs) emitted by shipped product702. This enables closed-loop controller 706 to effectively controlmaterial storage conditions within shipping container 700. Closed-loopcontroller 706 uses closed-loop control techniques to controlenvironmental variables, such as temperature, humidity, and aircirculation, while the shipped product 702 changes its VOC profile overtime and in response to the environmental variables. During operation,chemical sensor 704 continuously monitors the VOC profile and when itchanges, closed-loop controller 706 changes how the environment ismaintained to achieve certain outcomes such as preventing spoilage ofperishables.

In one example, when bananas or other produce are shipped they are keptin temperature-controlled and often environmentally controlledcontainers to prevent premature ripening. At the point of harvest,unripe bananas are packed into a refrigerated shipping container andheld at a low temperature to prevent ripening. This uses a lot ofenergy, which might not really be needed because the temperature controlis not based on any physical information from the banana other than theminimum temperature that bananas can tolerate without sufferingpermanent damage, and the date the banana was harvested. In contrast, ina refrigerated container that uses a VOC-sensor-based environmentalcontrol system, the initial setpoint temperature could be set higherthan the minimum that the bananas can tolerate, and the system couldhave a relatively large acceptable range of temperatures. Note that theVOC sensor system can be placed next to the refrigeration unit outsideof the temperature-controlled portion of the container. The sensor couldthen sample from the air before it passes through the refrigerationunit. If the VOC sensor system detects compounds that indicate thebananas are ripening, it can send a signal to the temperature controllerto either lower the setpoint temperature (which can either beincrementally lowered or immediately lowered to the minimum acceptablesetpoint), or adjust the control technique to minimize temperaturevariations. The setpoints can be adjusted to achieve the desired levelof ripening at the final shipping destination.

This type of shipping container facilitates enhanced supply chainmanagement, and potentially reduced storage times prior to the commodityarriving at the point-of sale. Based on VOC data, the temperature (orair flow) setpoints during the shipping process may be adjusted tominimize energy usage. The VOC information can also be used to shut offrefrigeration during shipment if the VOC information indicates that theproduct has spoiled, and can be abandoned to save energy. The VOC datacan also be provided to end users to validate shipment quality controlat all times and locations in the supply chain for a product. The VOCscan also be associated with steps on a pack line for postharvest sortingand shipping (e.g., sorting for various stages of ripeness).

In another example, the system reduces energy consumption inrefrigerated shipping containers by using closed-loop control systemsalong with chemical sensors. In this example, we will monitor for VOCsignatures off-gassed from food products in a shipping container asindirect indicators of quality and freshness. This information is usedto provide feedback to decrease/increase cooling capacity and/orventilation within the shipping container over time. By implementingthis sensor feedback into a closed-loop control system, the system isbetter able to tailor the cooling profile of the container to bothoptimize energy consumption as well as stably maintain the cargo at itsoptimum temperature over the duration of a shipment. As the food orproduce in the container changes over time (as detected by their VOCprofiles), the container environment can be optimized in near-real-time,without using energy for unnecessary cooling when it is not needed.

Note that VOCs are very good indicators of post-harvest food quality,and specific off-gassed compounds have been identified in many foodstuffs that are linked to age, ripeness, and quality of storageconditions. Current shipping container conditions are almost always heldat temperatures much lower than needed to ensure proper food storage.This extra “insurance” cooling allows the shipping industry to guaranteeshipment conditions to growers at the point-of-harvest. However, theextra power consumption due to this cooling “insurance” can bedramatically reduced if the temperature setpoint of the container can bedynamically adapted in response to cargo quality, instead ofartificially setting static low temperatures for the duration of thevoyage.

By detecting a multitude of off-gassed chemical compounds from food atthe same time, the system enables a more reliable assessment of producecargo freshness and the corresponding need of storage conditionadjustments in near-real-time. The abundance of these measured VOCs canbe used to tune a “smart” refrigerated cargo shipping system to reduceenergy consumption and simultaneously maintain the cargo by dynamicallyadjusting the container ambient conditions.

The shipping container can also be controlled to reduce food spoilage.In addition to single compounds (like ethylene) that indicate foodspoilage, the actual spoilage bacteria itself frequently contributes tothe ultimate mixture of volatiles generated by produce cargo. Detectionof microorganism-specific volatiles can serve as one of the mostimportant indications of additional cooling demand for improved storageconditions. For example, Pantoea agglomerans and Rahnella aquatilis areboth species of spoilage bacteria that have been isolated from mixedlettuce. Each bacteria strain produces a range of VOCs such as: ethanol,ethyl acetate, 2-methyl-1-propanol, 2-methyl-1-butanol,3-methyl-1-butanol, 2,3-butanedione, 3-methyl-1-pentanol, 1-butanol and1-hexanol. Under optimized storage conditions (e.g., airtight packing at7° C.), 2-methyl-1-butanol, 3 methyl-1-butanol and ethanol are producedalone by the spoilage microorganisms. If high concentrations of theabove-listed compounds are reached on the cut surfaces of shredded mixedlettuce, the quality of the shredded mixed lettuce can be negativelyinfluenced by the microbiological production of metabolites. Hence,detection of these compounds at an early stage can serve as a signal forthe modification of storage conditions, thereby saving the shipment andallowing for human consumption.

Likewise, a complex mixture of “alarm” volatiles are also known to beproduced during fish and meat spoilage. For example, in fish such aswhiting (Merlangius merlangus), cod (Gadus morhua) and mackerel (Scomberscombrus), as many as 86 VOCs have been previously simultaneouslyidentified. A total of 20 of these could be used to characterize“freshness” including: alcohols, ketones, aldehydes and C2-C11 esters.Detection of meat spoilage is also possible by measuring VOCs. Theconcentrations of multiple VOCs, particularly sulfur compounds, tend toincrease over the storage time. Some compounds, such as ethanol, aremore generally produced in various perishables during storage, and arepresent in greater amounts under non-optimal storage conditions. Infact, empirical evidence shows that a VOC-based metabolic profilingapproach possesses enough discriminatory information to differentiatenaturally spoiled pork from pork contaminated with Salmonellatyphimurium, a food poisoning pathogen commonly recovered from porkproducts.

Chemical analysis of mixtures of volatiles can provide comprehensiveinformation regarding cargo freshness and the need for storage conditionadjustment. However, the data may be excessively complex to directlyinterpret. To remedy this problem, data-mining and advancedsignal-processing techniques can be used for pattern recognitionassociated with spoilage prediction.

We now describe closed-loop control system 706, which is illustrated inmore detail in FIG. 8. As illustrated in FIG. 8, a chemical sensor inenclosed system 804 generates an output X₀ 806, which provides feedback808, which is compared against a reference signal X_(i) 802. When thechemical sensor system detects a specific compound or composite changesin the volatiles profile, an adjustment is made either to the referencesignal X_(i) or to the feedback loop.

For the system to operate, at least one environmental variable must beclosed-loop controlled (e.g., temperature, humidity, light, etc.)through a microcontroller or some other adjustable control method. Thecontrol system can either be continuous (PID, H2, etc.) or discrete(on-off control, etc.). Inside enclosed system 804, there is a productwhose off-gassed volatile profile varies over time and due to theenvironmental variables. An example is perishable material such as foodin a refrigerator that may emit volatiles due to onset of spoilage,ripening (e.g., for produce), etc. In this case, closed-loop controlsystem 706 aims to maintain adequate storage conditions while avoidingexcessive cooling, which requires a large energy expenditure. The systemtries to maintain a reference profile signal X_(i) 802 to preventspoilage-specific compounds from arising. Depending on the complexity ofthe profile signal, a computer (e.g., in smartphone form or a portablefactor) may need to be used to process the data and compare it againstthe reference signal. When the sampled signal varies from the referencesignal, the computer sends a signal to an environmental controller toadjust the control parameters.

Operating a Control System in a Shipping Container

FIG. 9 presents a flow chart illustrating operations performed by aclosed-loop environmental control system within a shipping container inaccordance with the disclosed embodiments. First, the system gatherssamples of compounds off-gassed from products stored in the shippingcontainer (step 902). Next, the system uses a chemical detector tomeasure concentrations of volatile compounds-of-interest in the samples(step 904). The system then performs closed-loop control of one or moreenvironmental parameters in the shipping container based on the measuredconcentrations (step 906). During operation, the system periodicallydetermines from the measured concentrations of the volatilecompounds-of-interest whether the products stored in the shippingcontainer have spoiled (step 908). If the products stored in theshipping container have spoiled, the system discontinues using power tocontrol the at least one environmental parameter (step 910).

Various modifications to the disclosed embodiments will be readilyapparent to those skilled in the art, and the general principles definedherein may be applied to other embodiments and applications withoutdeparting from the spirit and scope of the present invention. Thus, thepresent invention is not limited to the embodiments shown, but is to beaccorded the widest scope consistent with the principles and featuresdisclosed herein.

The foregoing descriptions of embodiments have been presented forpurposes of illustration and description only. They are not intended tobe exhaustive or to limit the present description to the formsdisclosed. Accordingly, many modifications and variations will beapparent to practitioners skilled in the art. Additionally, the abovedisclosure is not intended to limit the present description. The scopeof the present description is defined by the appended claims.

What is claimed is:
 1. A preconcentrator for preconcentrating gassamples for agricultural applications, comprising: multiplepreconcentrators that are programmable to separately sample duringdifferent time slots, each preconcentrator including a substrate thatcomprises: one or more channels for accommodating a sample flow, whereinthe one or more channels are coated with a sorbent material so that thesorbent material can be exposed to the sample flow; and one or moreheaters for heating the sorbent material.
 2. The preconcentrator ofclaim 1, wherein the sample flow includes one or more of: gas samplesoutgassed from plants in a greenhouse; gas samples outgassed from plantsin an orchard; gas samples obtained during post-harvest transportationof agricultural products; and gas samples obtained during post-harveststorage of agricultural products.
 3. The preconcentrator of claim 1,further comprising a pump that facilitates moving the sample flowthrough the sorbent material.
 4. The preconcentrator of claim 1, whereina sorbent type and a sampling temperature are controllable duringsampling to promote capture of volatile organic compounds of interestover extraneous chemicals.
 5. The preconcentrator of claim 1, furthercomprising an external cooling supply.
 6. The preconcentrator of claim1, wherein the one or more heaters trigger a release of absorbedcompounds from the sorbent material.
 7. The preconcentrator of claim 1,wherein the one or more heaters are fabricated by depositing aconductive material on the substrate.
 8. The preconcentrator of claim 1,wherein the one or more heaters uniformly heat an active area.
 9. Thepreconcentrator of claim 1, further comprising: one or more temperaturesensors; and a feedback-based temperature control system that usesreadings from the one or more temperature sensors to control the one ormore heaters.
 10. The preconcentrator of claim 1, wherein the one ormore channels comprise high-aspect-ratio, porous microstructures forholding the sorbent material.
 11. The preconcentrator of claim 10,wherein the high-aspect-ratio microstructures include channels that areabout 300 micrometers tall and 10 micrometers wide.
 12. Thepreconcentrator of claim 1, wherein the one or more heaters areprogrammable to do one or more of the following: apply heat rapidly toinstantly desorb chemicals from the sorbent material; and apply heatgradually to control a release of different compounds at different timesfrom the sorbent material.
 13. The preconcentrator of claim 1, whereinthe preconcentrator is fabricated using photolithography techniques. 14.The preconcentrator of claim 13, wherein the preconcentrator isfabricated using anisotropic wet-etch techniques.
 15. Thepreconcentrator of claim 1, further comprising: a sampler cartridgesystem comprising multiple sample cartridges, wherein: each said samplecartridge houses one of the multiple preconcentrators; and no more thanone cartridge at a time is positioned within the sample flow.
 16. Apreconcentrator for preconcentrating gas samples for agriculturalapplications, comprising: at least one substrate, each substrateincluding: one or more channels for accommodating a sample flow, whereinthe one or more channels are coated with a sorbent material so that thesorbent material can be exposed to the sample flow; and one or moreheaters for heating the sorbent material; an aerial platform capable offlight, wherein the aerial platform includes an airfoil; and an airintake, located in a field of air flow across the airfoil during flightof the aerial platform, for creating the sample flow.
 17. Thepreconcentrator of claim 16, further comprising: a cartridge systemcomprising multiple cartridges, wherein: each said cartridge houses oneof the at least one substrate; and no more than one cartridge at a timeis positioned within the sample flow.
 18. The preconcentrator of claim17, further comprising: a memory that stores a geolocation and a time atwhich each cartridge is exposed to the sample flow.
 19. Thepreconcentrator of claim 16, further comprising: an array of samplers,each sampler including one of the multiple preconcentrators; and one orboth of a solenoid and a manifold for directing the sample flow to nomore than one of the samplers at a time.